Abstract: ?1D-adrenergic receptors (ARs) are essential G protein-coupled receptors (GPCRs) of the sympathetic nervous system, and are a promising therapeutic target for an array of diseases. In the central nervous system, the ?1D-AR tightly regulates stimulus-induced locomotor activity, and is 1 of 13 hypermethylated genes associated with decreased brain volume in schizophrenic patients. The ?1D-AR is critical for blood pressure regulation and stenosis of damaged blood vessels. The receptor also can negatively impact urine flow by contracting the prostate in patients suffering from benign prostatic hypertrophy (BPH). Thus, ?1-AR antagonists (??-blockers?) are often used to treat hypertension, urinary incontinence, and most recently with promising success stories, to prevent reoccurring nightmares in combat veterans afflicted with Post-Traumatic Stress Disorder. Unfortunately, major toxicities can often occur in patients taking ?-blockers. During the ALLHAT trial, ?-blocker therapy was discontinued due to increased patient morbidity. Accordingly, a clearer picture of how the ?1D-AR engages with its cellular environment will provide critical insights towards the further development of small molecule ?1D-AR modulators beneficial for the treatment of PTSD, BPH, and cardiovascular disease. Surprisingly, our basic knowledge of ?1D-AR biochemical processes is lacking within human contexts, primarily because no human cell lines have been identified that express endogenous ?1D-ARs. Without adequate cell culture models and human model cell systems to examine their discrete biochemical interactions, it will continue to be challenging to develop new small molecules targeting ?1D-ARs and to understand their essential molecular and cellular functions. We have made significant progress towards solving some of these mysteries. First, we discovered that ?1D-ARs interact with multiple PSD95/DLG1/Zo-1 (PDZ) domain-containing proteins. Second, we found these interactions are essential for ?1D-ARs to be expressed as functional receptors at the plasma membrane. Remarkably, we found that ?1D-ARs interact with two PDZ- proteins, syntrophin and scribble, in all human cell lines we examined. This novel discovery provides an opportunity to develop small molecule allosteric ligands targeting ?1D-AR:PDZ-protein interaction-interfaces. However, this first requires a thorough characterization of ?1D-AR:PDZ-protein architecture and function. In this competing renewal, we propose to extend our findings in new directions using the following aims. Aim 1: Determine whether scribble organizes ?1D-ARs into signaling clusters. Aim 2: Identify ?1D-AR:PDZ-protein complex(es) in human cells. This proposal has the overarching goal of targeting discrete ?1D-AR:PDZ-protein interfaces with novel small molecules to treat diseases associated with aberrant ?1D-AR signaling.